Pathological vascular remodeling is a key component and frequently life-threatening consequence, of vascular diseases in both the systemic and pulmonary circulation. In a neonatal model of hypoxic pulmonary hypertension, we have previously reported tha We have previously reported that similar to humans with IPAH, hypoxia-induced pulmonary artery (PA) remodeling is associated with marked increases in the density of vasa vasorum (VV) network, recruitment and infiltration of circulating progenitor and inflammatory cells to the PA, implicating VV in disease pathogenesis. The long-term goal of our studies is to evaluate cellular mechanisms and endogenous molecular factors that mediate vasa vasorum neovascularization in hypoxia-induced pulmonary vascular remodeling. Extracellular adenine nucleotides are increasingly recognized as important regulators of vascular functions. We demonstrated that the adventitial vasa vasorum endothelial cells (VVEC) are a potent source of extracellular ATP, which acts as an autocrine/paracrine factor mediating hypoxia-induced VVEC angiogenesis. Our data demonstrated that exaggerated nucleotide-mediated angiogenic responses in VVEC involve activation of P2Y1, and P2Y13 purinergic receptors, PI3K/Akt/mTOR, ERK1/2, and the elevation of cytoplasmic, nucleoplasmic, and mitochondrial Ca2+. In addition, our preliminary data for this proposal we demonstrated the presence of subsets of P2Y13R expressing highly proliferative potential colony forming cells (VVECFC) in VVEC cultures, which might be responsible for angiogenic VV expansion. As the importance of cellular energy metabolism has been postulated to link cellular metabolic state and functional responses, in this proposal we will test the hypothesis that purinergic regulation of VV angiogenesis involves the activation of mitogenic and bioenergetic pathways in VVEC and VVECFC, leading to metabolic reorgnization/reprogramming and phenotypical changes in these cells towards differentiated endothelial phenotype. The studies proposed in three specific aims will: (i) Characterize a hierarchy of colony-forming cells residing in VVEC; determine their phenotype, proliferative and angiogenic capabilities; (ii) examine purinergic receptor-mediated signaling pathway in clonogenic, angiogenic, and signaling responses in VVEC and VVECFC; (iii) determine bioenergetic organization of VVEC and VVECFC and determine whether extracellular nucleotides and hypoxia induce angiogenic and phenotypic responses in these cells via energy metabolism and mitochondrial regulation. Ultimately, this research proposal aspires to translate fundamental questions of purinergic signaling to the clinically relevant problem of hypoxia-induced angiogenesis. Understanding of fundamental biological mechanisms of metabolic and signaling regulation of VV expansion to a functional vascular network will facilitate development of the innovative treatments for pulmonary hypertension and a variety of vascular diseases that involve impaired angiogenesis and pathologic vascular remodeling.